September is coming, so you know what that means. Kids are going back to school, football is back, pumpkin spice is invading every beverage known to mankind, and somewhere on the internet someone is warning you that the stock market is about to collapse.

Why? Because it’s September.

And to be fair, September has earned a pretty lousy reputation on Wall Street. According to the Stock Trader’s Almanac, since 1950 September has been the worst-performing month of the year for the S&P 500, Dow Jones Industrial Average, and several other major U.S. indexes.

Go back even further and the picture doesn’t get much prettier. Bloomberg data cited by J.P. Morgan shows that since 1928, the S&P 500 has averaged approximately -1.17% during September, making it the weakest month of the year over that period.

Sounds terrifying, right?

Well…not exactly.

The Worst Month Isn’t Necessarily a Bad Month

This is where statistics can be dangerous if we don’t put them into perspective. Saying September is historically the “worst month of the year” sounds like we’re preparing for the financial apocalypse. But an average decline of roughly 1% isn’t exactly the Great Depression.

The Stock Trader’s Almanac data since 1950 paints a similar picture. Historically, September has produced an average S&P 500 decline in the neighborhood of 0.5% to 0.7%, depending on the exact period measured.

That’s the important distinction. September isn’t historically bad because the market crashes every September. It’s bad because its long-term average return is slightly negative while most other months have historically produced positive average returns.

Of course, September has certainly delivered some punches over the years. The market experienced major September declines surrounding the terrorist attacks in 2001, the financial crisis in 2008, the debt-ceiling turmoil of 2011 and the 2022 bear market. Those events have helped reinforce September’s frightening reputation.

But here’s the problem: those weren’t selloffs caused by September. They were major economic, financial or geopolitical events that happened to occur during September.

September doesn’t wake up on the first trading day and decide to destroy your 401(k).

Why Does September Have Such a Bad Reputation?

There are several theories. Portfolio managers return from summer vacations and begin repositioning portfolios. Institutions may dump underperforming positions as the third quarter comes to an end. Trading volume increases after the slower summer months, and investors begin looking ahead toward earnings, economic data, Federal Reserve policy and the final quarter of the year.

The Stock Trader’s Almanac specifically points to portfolio managers “cleaning house” after Labor Day and portfolio restructuring approaching the end of Q3 as possible contributors to September weakness.

There’s another interesting wrinkle this year: 2026 is a midterm election year. Historically, September’s S&P 500 performance has actually improved slightly during midterm years. Stock Trader’s Almanac data going back to 1950 shows an average September decline of approximately 0.4% during midterm years. Still negative, but hardly a reason to build a bunker in the backyard.

Statistics Are Information, Not Instructions

This is where I think traders get themselves into trouble.

Knowing that September has historically been the worst month of the year is useful information. Automatically selling everything on August 31 because September is coming is something completely different.

Historical tendencies tell us what has happened. They don’t tell us what will happen.

If the S&P 500 is trending higher, economic data remains supportive, earnings are strong and your trading setup tells you to buy, should you ignore all of that because a calendar says September?

Of course not.

Likewise, if markets begin breaking important support levels, volatility increases and your trading plan tells you risk is increasing, you shouldn’t blindly buy because you think the “September Effect” is nonsense.

Trade what the market is actually giving you.

Don’t Let the Headlines Trade Your Account

This is especially important for newer traders because scary headlines generate clicks. “SEPTEMBER HAS HISTORICALLY AVERAGED A MODEST DECLINE” isn’t exactly going viral on YouTube.

“THE WORST MONTH FOR STOCKS IS HERE!” sounds much better.

Both statements can technically be true, but they create completely different emotional reactions.

Your job as a trader is to separate the data from the drama. September’s historical weakness is worth knowing. It may justify being a little more attentive to risk, position sizing and changing market conditions. What it does not justify is abandoning your trading plan because of a seasonal statistic.

If volatility increases, perhaps reduce your position size. If the market breaks support, respect it. If your setup isn’t there, don’t force a trade. And if the market continues moving higher despite September’s terrible reputation, don’t stand in front of it simply because history told you this month was supposed to be weak.

Markets don’t have to follow the averages.

That’s ultimately the lesson of the September Effect. History gives us context, not certainty. Understand the statistics, respect the historical tendency and prepare for the possibility of increased volatility—but then let price, risk and your trading plan determine what you actually do.

September may historically be Wall Street’s worst month.

That doesn’t mean it has to be yours.